1. Field of the Invention
The present invention relates to an apparatus for predicting remaining life of a battery mounted on a powertrain as a power source and an apparatus for warning of the end of life of the battery, and relates to a powertrain having the apparatuses installed therein.
2. Description of the Related Art
Here, a term “powertrain” refers to a vehicle in which a battery is used as a part of a power source or used as the power source itself. The vehicle includes, for example, a hybrid vehicle powered by combined use of a gasoline engine and an electric motor similarly to a hybrid system, an electric vehicle powered by a fuel cell, and other known or to be developed vehicles having a battery used as a power source.
A major feature of a hybrid system in a hybrid vehicle is that a gasoline engine and an electric motor are selectively used in accordance with vehicle running conditions, to make full use of the advantages of the gasoline engine and the electric motor while compensating for their disadvantages. Accordingly, a usage pattern of a battery installed in the hybrid vehicle varies depending on running conditions of the vehicle. Specifically, at the time of starting the vehicle or during light load running with poor engine efficiency, for example, the vehicle is mainly powered by the electric motor while making full use of the battery. On the other hand, the vehicle is mainly powered by the gasoline engine during medium-speed low-load running with good engine efficiency, and under acceleration, the gasoline engine is increased in output and assisted by the electric motor as required. Accordingly, the battery is used less during the medium-speed low-load running and under-acceleration. Under deceleration, the electric motor is caused to function as a generator in order to convert kinetic energy of the vehicle into electrical energy for regenerative braking. The converted electrical energy is stored in the battery and reused under acceleration or on other occasions. Thus, the battery used in the hybrid vehicle is discharged under acceleration and charged by the regenerative braking under deceleration, and the charge and discharge of the battery are repeated while the vehicle is running.
A battery installed as a power source in a powertrain deteriorates with time through normal usage, and the life of the battery expires at some point in time because the capability of charging/discharging a cell (a battery capacity) gradually drops as internal resistance of the battery increases due to prolonged running. It is therefore necessary for conditions of the battery in the powertrain to be appropriately kept track of.
Factors influencing age deterioration of a battery include vehicle characteristics, battery environment, power consumed by electrical components, and vehicle running conditions. The vehicle characteristics refer to characteristics relating to a vehicle type, such as, for example, a model year, a vehicle weight, and device specifications. The device specifications refer to, for example, types and capacities of an engine, and electrical components, such as an air conditioner, mounted on the vehicle. The vehicle type and the device specifications are connected with consumption of the battery in the vehicle, thereby being viewed as an influential factor on battery deterioration. The battery environment refers to environment around the battery including a temperature of the battery, an ambient temperature, humidity, and the like. Overcharging or over discharging of the battery promotes battery deterioration. Because over-discharge or overcharge of the battery promotes deterioration, the over-discharging and overcharging are regarded as influential factors on battery deterioration. The electrical components consuming power includes the air conditioner, audio equipment, and other electrical power consuming components mounted on the vehicle. These electrical components are counted as influential factors on battery deterioration because the components use electrical power accumulated in the battery. Further, the vehicle running conditions are related to, for example, a running distance, driving operation of the vehicle, and the like. Because increases of the running distance generally leads to increased battery deterioration, the running distance is regarded as a factor influencing battery deterioration. The degree of battery deterioration varies depending on vehicle driving operation performed by a driver.
As a conventional technique relating to battery deterioration, a system is disclosed in which variations in charge and discharge features among cells are detected to give an advance warning, thereby urging a driver to perform equalizing charge. The cells of a battery do not deteriorate equally with respect to the charge and discharge features, but become deteriorated to varying degrees from cell to cell with respect to charge and discharge features. In view of the fact that the variations which have grown excessively large greatly affect life expectancy of the battery, the advance warning is provide to the driver in the above-described system. When the advance warning is issued, the cells can be refreshed so as to be in a fully charged state by means of low-voltage currents fed into the cells for a prolonged time from an external battery recharger.
As a method for evaluating age deterioration or life expectancy of a battery cell, a method for removing a power output device having a battery to be evaluated and evaluating the removed power output device on a test bench and a method for conducting the evaluation in a running test of an actual vehicle have been conventionally known. The running test of an actual vehicle contains a simulated running test conducted in a laboratory under predetermined experimental conditions and an actual running test conducted using an actual vehicle operated in predetermined driving patterns including metropolitan highway running, urban area running, rough road running and others. Further, a method for directly detecting the capabilities of charging and discharging a battery to determine the degree of battery deterioration and life expectancy of the battery is also known as one of the evaluation methods.
For example, Japanese Patent Laid-Open Publication No. Hei 10-123018 discloses a running test facility of chassis dynamometer type for testing an electric vehicle, and Japanese Patent Laid-Open Publication No. 2000-234984 discloses a performance evaluation system for evaluating a power output device taking into account effects exerted by accessory devices in a vehicle. Further, Japanese Patent Laid-Open Publication No. Hei 6-163084 discloses a method for measuring remaining life of an accumulator battery used for a motor-driven vehicle, and Japanese Patent Laid-Open Publication No. 2005-137091 discloses a display for a vehicle-mounted battery.
In the running test facility disclosed in the Publication No. Hei 10-123018, a vehicle placed on front and rear rollers is driven in a state where a dummy running resistance is exerted on the vehicle using a running resistance generation mechanism to conduct a running test under conditions similar to those of actual running. As a result of the test conducted on an electric vehicle using the running test facility, the efficiency with which supplied power is incorporated into a drive force (running efficiency), a travel range attained in a typical running mode, and the level of a voltage drop in the battery can be determined.
FIG. 9 shows process steps performed in the performance evaluation system for evaluating a power output device disclosed in the Publication No. 2000-234984. Because, in the running test of an actual vehicle, the entire vehicle is subjected to the test, the factors having an effect on performance of the power output device are great in number and in complexity, which causes a problem in accuracy of evaluated data. On the other hand, in the method for removing only the power output device and evaluating the power output device on the test bench, the accessory devices, such as an air conditioner, mounted on the vehicle are not equipped to the test bench, which causes a problem in that effects exerted by the accessory devices remain undetected and constitute an error of the test. Accordingly, in the method for evaluating performance of the power output device disclosed in the above Japanese Patent, data concerning running of a vehicle equipped with the power output device is collected during actual road running and in a running test (S10). Then, operation of the power output device during the running test of the actual vehicle is reproduced in the evaluation system (S12). Data to be evaluated is output (S14), and the performance of the power output device is evaluated using the output data (S16). In the performance evaluation system, the effects exerted by the accessory devices in the vehicle can be included in the evaluation.
In the method for measuring remaining life of an accumulator battery for a motor-driven vehicle according to the above-described Publication No. Hei 6-163084, a voltage value of the accumulator battery for a motor-driven vehicle attained relative to a predetermined discharged capacity during a vehicle run is obtained for each run, and an estimated number of runs until a predetermined end-of-life voltage is attained is obtained using a relational equation between the number of runs and the voltage value. Then, the remaining life is determined from a difference between the estimated number of runs and the number of runs performed at the present time.
The display for a vehicle-mounted battery of the above-described Publication No. 2005-137091 is a device for retrieving voltage-current information at the time of charging and discharging a battery, to compute deterioration information referring to a plurality of charge and discharge voltage-current characteristics corresponding to the degree of deterioration of the battery prestored in a memory means.
As described above, a wide variety of factors affect age deterioration of a battery in a powertrain, and the factors vary depending on the circumstances. To estimate durable years and the degree of deterioration of a battery, it is necessary to take into account all the factors in a comprehensive manner. Because an error contained in an estimation based on only a specific one of the factors is extremely great, the estimation based on such a specific factor is not appropriate for practical use.
The results obtained from vehicle running tests described in the above Publications No. Hei 10-123018 and No. 2000-234984 show age deterioration of a battery only under fixed conditions. Because an actual vehicle run or battery environment generally changes in a complicated manner, the result of a running test cannot be applied to an actual vehicle run without being processed. Thus, it is inappropriate to determine life expectancy of a battery only from numerical values of a running distance of a vehicle, a period of use, or the like, because a greater error will be introduced by such determination.
Because the above-described warning system for urging a driver to perform equalizing charge does not cover age deterioration in capability of charging and discharging the cells as a whole, such a warning system is regarded neither as a device for predicting remaining life of a battery in a powertrain nor a device for warning a driver that the battery has reached the end of its life.
On the other hand, in the methods for directly detecting the capabilities of charging and discharging a battery to determine the degree of deterioration or life expectancy of the battery as described in the above-described Publications No. Hei 6-163084 and No. 2005-137091, it is possible to detect a state of the battery by measuring voltages and currents during charge and discharge operations, but impossible to reliably predict life expectancy of the battery.
Although it is important to keep track of battery conditions in a powertrain, means for predicting or warning of the battery conditions does not exist under present circumstances. In a hybrid vehicle, because the engine functions as an electricity supplier to maintain the battery in a constant charged state during operation without the need to recharge the battery from an external supplier, a driver is less aware of battery life, which provides further problems as described below.
For example, even when capabilities of charging and discharging a battery become deteriorated in a hybrid vehicle having a gasoline engine and an electrical motor as power sources, the gasoline engine automatically compensates for the deterioration, usually without a driver being aware of it. A lack of awareness of battery deterioration forces the gasoline engine having a capacity which is generally smaller than that of a vehicle powered only by a gasoline engine to continue compensating for the deterioration, resulting in poor fuel economy. Further, the lack of awareness of battery deterioration raises a risk that the vehicle will become inoperable due to the end of battery life during a long-distance drive.